Unraveling the Mechanisms of Polyethylene Thermal Oxidation Influenced by TiO2 and ZnO: A Combined Experimental and Computational Study

Incorporating fillers into polyethylene (PE) has emerged as a crucial strategy for modulating its thermo-oxidative aging. However, the mechanistic differences among various fillers remain insufficiently understood at the atomic level. To address this issue, this study combines ab initio molecular dynamics (AIMD), first-principles calculations, and thermo-oxidative experiments to investigate the effects of two commonly used fillers, TiO₂ and ZnO, on the thermo-oxidative aging of PE. The results reveal that both fillers promote the dissociation of C–H bonds of PE. TiO₂ enhances the formation of alkyl radicals, driving the generation of hydroxyl and carbonyl groups on the polymer chains. In contrast, ZnO, with its inherently less stable surface structure, exhibits a stronger effect on C–H bond dissociation, leading to significant crosslinking reactions in PE and the development of vinyl groups. These groups are less reactive toward oxygen (O₂), hindering the formation of hydroxyl and carbonyl groups by reducing the density of reaction sites between O₂ and carbon chains. Understanding the intricacies and mechanisms of these processes not only deepens our knowledge of the fundamental aspects of PE's thermo-oxidative aging but also provides a basis for designing fillers to effectively regulate its aging behavior.